Implementation of the X-centric pulse sequence at low field for MRI of water penetration in clay
Bibliographic record
Abstract
Although the relaxation time constants of free water are relatively long, the relaxation of water in concrete and other sedimentary materials is significantly shorter. Dissolved ions and porous environments can cause increased magnetic susceptibility effects, leading to the apparent transverse relaxation time T 2 ⁎ of this water to decrease drastically, from seconds to less than a millisecond. The longer T 2 ⁎ of the low field regime (less than 0.5 T) should allow for 2D and even 3D imaging of water content in these types of materials; developing a suitable technique for imaging of short- T 2 ⁎ samples would permit imaging of porous rocks and concrete. A 12 mL wet bentonite clay sample was placed within a syringe and allowed to absorb increasing volumes of standing water. This progressing absorption was imaged on a 73.5 mT magnetic resonance imaging (MRI) system using the X-Centric pulse sequence. This pulse sequence is a modified version of the common gradient echo (GE) pulse sequence, in which each half of k -space is acquired separately, from the centre outwards in the readout direction, ensuring minimal T 2 ⁎ -weighting of the resulting image and allowing for 2D imaging within the short time frame of the shorter T 2 ⁎ of water in the clay. Bulk relaxation measurements of T 2 ⁎ and the longitudinal relaxation time T 1 were performed for increasing water content, with a mean T 1 of 12.0 ± 1.1 ms and mean T 2 ⁎ of 4.5 ± 0.7 ms; 2D imaging of the clay sample was performed with both GE and X-Centric. In addition, a 2D T 2 ⁎ map was generated from eight X-Centric images taken at different echo times. The X-Centric pulse sequence was demonstrated to be an effective imaging method for short signal-lifetime samples, such as water trapped in bentonite clay. The ease of implementation, minimal diffusion-weighting and T 2 ⁎ weighting of the k -space centre, and considerable gains in signal-to-noise ratio and imaging efficiency position this pulse sequence as a viable alternative or complement to conventional GE acquisitions. Additionally, the short echo-time of the X-Centric pulse sequence allows it to be used effectively with non-proton MRI, including 23 Na and fluorinated gases (e.g., 19 F) where the T 2 ⁎ -decay is a potentially significant source of signal decay.
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How this classification was reachedexpand
Full frame distilled prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. Learned from the 10,348 direct Codex labels and 10,348 direct Gemma labels. Candidate is the union of thresholded teacher heads; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels or direct frontier model labels.
Codex and Gemma teacher scores by category
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.000 | 0.000 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.000 | 0.000 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.000 | 0.000 |
Machine scores (provisional)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from itClassification
machine, unvalidatedMachine predicted; a candidate call from one teacher head, not a consensus.
How this classification was reached, model by model and score by score, is at the end of the page under "How this classification was reached".